1. Field of the Invention
The present invention relates to a plasma processing apparatus used for manufacturing a semiconductor device.
2. Description of the Prior Art
A conventional plasma processing apparatus which utilizes the interaction between an electric field and a magnetic field for manufacturing a semiconductor device is described in Japanese Patent Laid-Open No. 2-51228. The arrangement of this prior art will be described below with reference to FIG. 1.
FIG. 1 is a sectional view showing an arrangement of a conventional plasma processing apparatus described in the above publication. This plasma processing apparatus is used as a dry etching apparatus and has a high-frequency electric field generating mechanism and a magnetic field generating mechanism which are in a reaction vessel 1. In addition, the reaction vessel 1 has an inlet port (not shown) for receiving an etching gas and an exhaust port 1a for exhausting the gas.
The high-frequency electric field generating mechanism has a pair of opposed electrodes constituted by an upper electrode 2 and a lower electrode 3, and a high-frequency power supply 4 for supplying a high-frequency power to these electrodes. The magnetic field generating mechanism is constituted by a plurality of magnetic field generating coils 5 arranged to surround the pair of electrodes 2 and 3. The magnetic field generating coils 5 are constituted by, e.g., solenoid coils 5a to 5f, and are connected to pulse power supplies 6a to 6f of a pulse voltage generator 6, respectively.
Dry etching performed by the plasma processing apparatus arranged as described above is performed as follows.
A wafer 7 serving as a material to be etched is placed at a predetermined position on the lower electrode 3, and an etching gas is supplied into the reaction vessel 1. At the same time, the etching gas is exhausted from the exhaust port 1a, and the pressure in the reaction vessel 1 is controlled to be a predetermined gas pressure.
In this state, when a high-frequency power is supplied from the high-frequency power supply 4 to the lower electrode 3, a high-frequency electric field having a direction indicated by an arrow E is formed between the electrodes 2 and 3 so as to produce a plasma 8. At this time, when periodic pulse voltages from the pulse voltage generator 6 are applied to the solenoid coils 5a to 5f serving as the magnetic field generating coils 5, a periodic magnetic field is generated in the direction indicated by an arrow F perpendicular to the high-frequency electric field. For this reason, the electric field and the magnetic field which are perpendicular to each other act on electrons in the plasma 8 to cause the electrons to perform cycloid movement, and the etching gas is effectively dissociated, thereby improving dissociation efficiency. In this manner, dry etching is performed for the wafer 7.
In this prior art, pulse voltages are periodically applied from the pulse voltage generator 6 to the magnetic field generating coils 5, and the ratio or the like of these pulse voltages is changed, thereby controlling the strength of a magnetic field or the uniformity of the distribution of the magnetic field.
In recent years, with an increase in degree of the integration density of a semiconductor device, a highly precise patterning technique becomes important. For this reason, a dry etching technique which can be used at a low pressure, can obtain a high etching rate, and is free from damage is required and dispensable.
However, in a plasma processing apparatus having the above arrangement, the following problems are posed. That is, magnetic field control is complicate, and the gate oxide film of a wafer is degraded or broken down due to localization of the charges of charged particles (charge-up damage).
More specifically, in the above plasma processing apparatus, a pulse voltage generator 6 and the plurality of magnetic field generating coils 5 arranged to surround the pair of electrodes 2 and 3 are used as the magnetic field generating mechanism. For this reason, the plurality of pulse power supplies 6a to 6f must be controlled to make a magnetic field on the surface of the wafer 7 uniform, resulting in complex magnetic field control. In addition, since the magnetic field generated by the magnetic field generating coils 5 is parallel to the surface of the wafer 7, charged particles are localized by the interaction between the electric field and the magnetic field. For this reason, nonuniformity of charges occurs on the surface of the wafer 7. This nonuniformity of charges may cause charge-up damage.